Sadly, this instrument now seems to be suffering from 'bit rot' as the data coming out the IEEE port seems sort of consistently garbled. For example a working instrument might return "0.000010 V DC" but this instrument might return "2134.334 !V DC". All ranges are mangled in a similar way (the exclaimation mark rather than space, the decimal point in the wrong place and wildly fluctuating readings).
I will swap the EPROM with my working instrument, assuming they have the same hardware.
dc